The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Genetic evidence of widespread differential selection for color vision among nocturnal lemurs


1Department of Anthropology, University of Texas at Austin, 2Molecular Genetics, Henry Doorly Zoo

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Color vision loss in nocturnal primates has been traditionally linked to a nocturnal lifestyle. However, recent work identified differential selection among nocturnal primates, with some species exhibiting selection to maintain dichromatic color vision at night. Our goals were to (1) determine the extent of differential selection on the S-opsin gene among nocturnal lemurs and (2) explore possible ecological factors driving differences in selection. We obtained DNA from wild individuals (n=126) representing 20 species and 5 genera (Avahi, Lepilemur, Cheirogaleus, Microcebus, Phaner), sampling populations from diverse habitats. We examined genetic signatures of selection at the population and lineage levels in order to estimate recent and more ancient selection pressures. At the population level, we compared the frequency, distribution and nucleotide diversity of replacement and silent mutations present within each population between congeners from different habitats. At the lineage level, we compared the ratio of replacement (dn) to synonymous (ds) substitution rates in coding regions between evolutionary lineages.

Our results suggest that differential selection on the S-opsin gene is widespread across nocturnal lemurs. Most variation is found between congeners, with some populations exhibiting evidence of purifying selection to maintain function while others exhibit relaxed selection and possible S cone loss. Comparing population and lineage results suggests this relaxation is relatively recent for many lineages. Habitat preference (open-canopy vs. rainforest) appears to influence selection in some genera. These results provide further evidence that many nocturnal primates maintain functional color vision, suggesting that specific ecological factors favor dichromacy even at nocturnal light levels.

Project was supported by a National Science Foundation Doctoral Dissertation Improvement Grant (#0752692), a Sigma Xi Grant in Aid of Research, and a University of Texas at Austin Liberal Arts Graduate Research Fellowship.

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